Structural Engineering Research Institute

Goyang, South Korea

Structural Engineering Research Institute

Goyang, South Korea
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Choi E.,Hongik University | Kim D.,Hongik University | Lee J.-H.,Daegu University | Ryu G.-S.,Structural Engineering Research Institute
Composites Part B: Engineering | Year: 2017

The aim of this study is to assess the pullout resistance of superelastic shape memory alloy (SMA) short fibers with different end shapes, which provide different anchoring actions, through monotonic and hysteretic pullout tests. For this study, NiTi superelastic SMA wire with a diameter of 1.0 mm was prepared and cut by a length of 40 mm to make SMA short fibers. Four types of SMA fibers with different end shapes were manufactured namely: 1) straight end shape, 2) crimped end, 3) bended end with L-shape, and 4) spearhead end. The straight end-shaped fiber was one without any anchoring action on the end part. The crimped fiber had grooves on the two sides manufactured by crimping an end part of 5 mm. The end-bended fiber had an L-shaped end with a 30° bending angle. The fiber with a spearhead was manufactured by pressing the end part of 5 mm. The pullout tests of the fibers from the mortar matrix were first monotonically conducted with displacement control, and the hysteretic pullout behavior was obtained by 4 cyclic loadings. The L-shaped fibers increased the pullout resistance significantly compared with the straight and crimped fibers. However, they did not reach the upper plateau stress of the SMA fiber to induce state transformation. Only the fibers with a spearhead end exceeded the stress for the state transformation because they provided sufficient anchoring resistance due to the spearhead. The maximum pullout resistance of the spearhead fiber was 3.74 times that of the L-shaped fiber. Moreover, they showed flag-shaped behavior during the hysteretic tests. © 2016 Elsevier Ltd

Kim J.-T.,Pukyong National University | Sim S.-H.,UNIST | Cho S.,University of Seoul | Yun C.-B.,KAIST | Min J.,Structural Engineering Research Institute
Structural Monitoring and Maintenance | Year: 2016

In this paper, recent research trends and activities on structural health monitoring (SHM) of civil infrastructure in Korea are reviewed. Recently, there has been increasing need for adopting smart sensing technologies to SHM, so this review focuses on smart sensing, monitoring, and assessment for civil infrastructure. Firstly, the research activities on smart sensor technology is reviewed including optical fiber sensors, piezoelectric sensors, wireless smart sensors, and vision-based sensing system. Then, a brief overview is given to the recent advances in smart monitoring and assessment techniques such as vibration- based global monitoring techniques, local monitoring with piezoelectric materials, decentralized monitoring techniques for wireless sensors, wireless power supply and energy harvest. Finally, recent joint SHM activities on several test beds in Korea are discussed to share the up-to-date information and to promote the smart sensors and monitoring technologies for applications to civil infrastructure. It includes a Korea- US joint research on test bridges of the Korea Expressway Corporation (KEC), a Korea- US- Japan joint research on Jindo cable- stayed bridge, and a comparative study for cable tension measurement techniques on Hwamyung cable-stayed bridge, and a campaign test for displacement measurement techniques on Sorok suspension bridge. © 2016 Techno-Press, Ltd.

Yoo D.-Y.,Hanyang University | Park J.-J.,Structural Engineering Research Institute | Kim S.-W.,Structural Engineering Research Institute
Composite Structures | Year: 2017

This study investigated the effects of fiber type and matrix strength on the fiber pullout behavior of high-performance fiber-reinforced cementitious composites (HPFRCC). The correlation between single fiber pullout behavior and flexural behavior of HPFRCC was also evaluated. Two different steel fibers, i.e., straight and hooked steel fibers, and three different matrix strengths were adopted. Test results indicate that the fiber pullout performance was improved with increasing matrix strength. The hooked fibers exhibited higher bond strengths and pullout work than the straight fibers, but at large slips, they showed smaller shear stress at the interface than their counterpart. In addition, the straight fibers were more effective in improving the pullout performance with the matrix strength than the hooked fibers. For the straight fibers, the shorter fibers provided higher bond strengths and maximum shear stress at the interface than the longer fibers. The flexural performance of HPFRCC beams was improved with increasing matrix strength. The beams with medium-length straight fibers (lf/df = 19.5/0.2 mm/mm) gave the best flexural performance, whereas those with hooked fibers exhibited the worst flexural performance. Due to several influential factors, the correlation between the single fiber pullout behavior and flexural behavior of HPFRCC beams was quite low. © 2017 Elsevier Ltd

Park Y.-S.,Structural Engineering Research Institute | Kim S.,Sejong University | Kim N.,Sejong University | Lee J.-J.,Sejong University
Engineering Structures | Year: 2017

A novel technique to evaluate the bridge boundary condition using neural networks is proposed. It can be used to establish a more accurate finite element (FE) model considering the behaviors of boundary conditions. In the proposed method, the aging and constraining effect of the boundary condition is represented by an artificial rotational spring at each support. A relationship between the responses of the bridge and the rotational spring constant is analytically investigated. This relationship can be used to estimate the rotational spring constant of the bridge using neural networks. The proposed method was verified through laboratory tests and field tests on a steel girder bridge. The proposed method can estimate the bridge boundary conditions directly from the actual behaviors of bridge supports, and this can effectively reduce the uncertainty of boundary conditions in FE model updating. © 2017 Elsevier Ltd

Yoo D.-Y.,Hanyang University | Ryu G.-S.,Structural Engineering Research Institute | Yuan T.,Korea University | Koh K.-T.,Structural Engineering Research Institute
Cement and Concrete Composites | Year: 2017

This study aims to reduce the cracking potential of posttensioning high-performance grout (HG) through use of shrinkage-reducing admixture (SRA). With this regard, an HG mixture was initially developed to possess appropriate fluidity with low bleeding and settling. Various amounts of SRA were subsequently incorporated into the developed HG mixture at 1% and 2% by weight to the cementitious components. A widely used ordinary grout (OG) mixture was also considered for comparison. Test results indicated that the HG mixture exhibited similar flowability to the OG mixture, while imparting much better performance with regard to strength, bleeding, and settling. The addition of SRA to the HG mixture led to higher compressive and tensile strength values after 28 days, lower shrinkage strain, lower maximum internal temperature due to hydration heat, and delayed shrinkage cracking. On the other hand, the degree of restraint due to an uneven surface of duct and the filling capacity of the HG were insignificantly affected by the inclusion of the SRA. Complete filling of ducts was observed for the HG samples. The OG mixture exhibited the smallest shrinkage strain and the best performance with regard to shrinkage cracking resistance; however, the OG mixture resulted in insufficiently filled ducts, leading to atmospheric exposure of prestressing strands. Consequently, the HG mixture with 2% SRA was proposed to be most appropriate for posttensioning grout with regard to the several properties denoted above. © 2017 Elsevier Ltd

Jang H.-O.,Hanyang University | Lee H.-S.,Hanyang University | Cho K.,Structural Engineering Research Institute | Kim J.,Hanyang University
Construction and Building Materials | Year: 2017

As a part of an ongoing research to develop construction joints using ultra-high performance concrete (UHPC) and reinforcements, shear performance of plain concrete construction joints is experimentally examined with push-off tests. Two different sets, namely, a combined set of UHPC (180 MPa) and a set of UHPC (180 MPa) and NSC (normal strength concrete, 30 MPa) were considered, each of which had five cases of interface treatment including use of water jet, vertical joint, and three cases of a grooved joint. In addition, cases without any construction joint were also considered as a reference. Key factors affecting shear performance of individual construction joint were investigated in terms of shear strength, failure mechanism, and displacement responses. Experimental results show that steel fibers and grooved geometry greatly affect shear performance for the combined set of UHPC, while interlocking mechanism of coarse aggregates is crucial for the set of UHPC and NSC. © 2017 Elsevier Ltd

Yoo D.-Y.,Hanyang University | Kim M.J.,Hanyang University | Kim S.-W.,Structural Engineering Research Institute | Park J.-J.,Structural Engineering Research Institute
Construction and Building Materials | Year: 2017

This study investigates the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) with single and hybrid steel fibers. To do this, three different types of steel fibers, i.e., hooked, twisted, and straight fibers, were considered, and a UHPFRC commercially available in North America was used as a comparison. To suggest a low-cost UHPFRC exhibiting the best flexural performance, test data and cost of fibers were analyzed based on a literature review. Test results indicate that straight steel fibers provide the best flexural performance, including strength, deflection capacity, energy absorption capacity, and cracking behavior, compared with hooked and twisted fibers, especially when many fibers (2% by volume) were incorporated. Hybrid reinforcement (hooked + straight fibers) efficiently improved the flexural performance of the UHPFRC with single hooked fibers, but the twisted + straight fibers were less effective than the UHPFRC with single twisted fibers. The optimum UHPFRCs contained 2 vol% single straight steel fibers (lf/df of 19.5/0.2) or hybrid 0.5 vol% long (lf/df of 30/0.3) and 1.5 vol% medium-length (lf/df of 19.5/0.2) straight steel fibers; they showed better flexural strength and cost effectiveness than other types of UHPFRCs. © 2017 Elsevier Ltd

Lee H.-S.,Hanyang University | Jang H.-O.,Hanyang University | Cho K.-H.,Structural Engineering Research Institute
Materials | Year: 2016

This study set out to derive the optimal conditions for ensuring the monolithicity of ultra-high-performance concrete (UHPC). Direct shear tests were performed to examine the influence on the bonding shear performance. The experimental variables included tamping and delay, which were set to 0, 15, 30, and 60 min. SEM and XRD analyses of the microstructure and composition were performed. The direct shear tests showed that the bonding shear strength was enhanced by the addition of tamping. For the normal-strength concrete (NSC), it is thought that a monolithicity of around 95% can be attained with a cold joint formation delay up to 60 min. In contrast, while the normalized bonding shear strength reduction of UHPC with a delay of 15 min was the lowest at around 8%, a dramatic degradation in the bonding shear performance was observed after 15 min. XRD analyses of the middle and surface sections revealed the composition of the thin film formed at the surface of the UHPC and, as a result, the main component appeared to be SiO2, which is believed to be a result of the rising of the SiO2-based filler, used as an admixture in this study, towards the surface, due to its low specific gravity. © 2016 by the authors.

Kim T.-H.,Structural Engineering Research Institute | Park K.-T.,Structural Engineering Research Institute
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

The recent constructed structures are featured by the combination of their functions and shapes as well as by their enlarged dimensions, which increase the demand for Structural Health Monitoring technology. Since every structure bears unique dynamic characteristics and is exposed to diverse external forces, various methods are studied to monitor the health of the structure. This study applies the Hilbert-Huang transform, the variance analysis and the edge detection method on the acceleration response of the structure to identify the initiation time of the abnormal behavior in which the structure experiences abnormal vibration. A scaled cable-supported bridge model is fabricated and subjected to cable failure test from which data before and after the occurrence of the abnormal behavior are acquired and compared to validate the proposed anomaly-extraction technique. © 2016 SPIE.

Park M.-S.,Structural Engineering Research Institute | Jeong Y.-J.,Structural Engineering Research Institute | You Y.-J.,Structural Engineering Research Institute
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2016

The offshore wind energy has gained attention from many countries to find alternative and reliable energy sources. Therefore, many offshore wind farms are in the planning phase. In order to increase the gross generation of wind turbines, the size of a tower and a rotor-nacelle becomes larger. In other words, the substructure for offshore wind turbines is strongly influenced by the effect of wave forces as the size of substructure increases. In the present study the hybrid substructure, which is composed of a multi-cylinder having different radius near free surface and a gravity substructure at the bottom of multi-cylinder, is suggested to reduce the wave forces. In addition, since a large offshore wind turbine has a heavy dead load, the reaction forces on the substructure become severe, thus very firm foundations should be required. Therefore, the dynamic pile-soil interaction has to be fully considered. In the present study the ENSOFT Group V7.0 is used to calculate the stiffness matrices on the pile-soil interaction conditions. Using the stiffness matrices and the loads at TP, which is obtained from GH-Bladed, the structural analysis of the hybrid substructure is carried out through ANSYS ASAS. The structural strength and deformation is evaluated to investigate an ultimate structural safety and serviceability of hybrid substructure for various soil conditions. The first few natural frequencies of substructure are heavily influenced by the wind turbine. Therefore, the modal analysis is carried out through GH-Bladed to investigate the resonance between the wind turbine and the hybrid substructure. © Copyright 2016 by the International Society of Offshore and Polar Engineers (ISOPE).

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